<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    <style>
        input{

            /* 聚焦时 蓝色边框 */
            outline: none;
        }
        input:focus{
            width: 200px;
            height: 100px;
        }

    </style>
</head>
<body>
    <!-- 主要针对 输入框   -->

    <!-- focus  获取焦点时  
    js当中 blur  失去焦点时 -->
    <input type="text">
</body>
</html>